Molecular control of PtdIns(3,4,5)P3 signaling in neutrophils

Nepalese indoor cookstove smoke extracts alter human airway epithelial gene expression, DNA methylation and hydroxymethylation

Household air pollution caused by inefficient cooking practices causes 4 million deaths a year worldwide. In Nepal, 86% of the rural population use solid fuels for cooking. Over 25% of premature deaths associated with air pollution are respiratory in nature. Here we aimed to identify molecular signatures of different cookstove and fuel type exposures in human airway epithelial cells, to understand the mechanisms mediating cook stove smoke induced lung disease. Primary human airway epithelial cells in submerged culture were exposed to traditional cook stove (TCS), improved cook stove (ICS) and liquefied petroleum gas (LPG) stove smoke extracts. Changes to gene expression, DNA methylation and hydroxymethylation were measured by bulk RNA sequencing and HumanMethylationEPIC BeadChip following oxidative bisulphite conversion, respectively. TCS smoke extract alone reproducibly caused changes in the expression of 52 genes enriched for oxidative stress pathways. TCS, ICS and LPG smoke extract exposures were associated with distinct changes to DNA methylation and hydroxymethylation. A subset of TCS induced genes were associated with differentially methylated and/or hydroxymethylated CpGs sites, and enriched for the ferroptosis pathway and the upstream regulator NFE2L2. DNA methylation and hydroxymethylation changes not associated with a concurrent change in gene expression, were linked to biological processes and molecular pathways important to airway health, including neutrophil function, transforming growth factor beta signalling, GTPase activity, and cell junction organisation. Our data identified differential impacts of TCS, ICS and LPG cook stove smoke on the human airway epithelium transcriptome, DNA methylome and hydroxymethylome and provide further insight into the association between indoor air pollution exposure and chronic lung disease mechanisms.

Neutrophil Activated by the Famous and Potent PMA (Phorbol Myristate Acetate)

This review will briefly outline the major signaling pathways in PMA-activated neutrophils. PMA is widely used to understand neutrophil pathways and formation of NETs. PMA activates PKC; however, we highlight some isoforms that contribute to specific functions. PKC α, β and δ contribute to ROS production while PKC βII and PKC ζ are involved in cytoskeleton remodeling. Actin polymerization is important for the chemotaxis of neutrophils and its remodeling is connected to ROS balance. We suggest that, although ROS and production of NETs are usually observed together in PMA-activated neutrophils, there might be a regulatory mechanism balancing both. Interestingly, we suggest that serine proteases might determine the PAD4 action. PAD4 could be responsible for the activation of the NF-κB pathway that leads to IL-1β release, triggering the cleavage of gasdermin D by serine proteases such as elastase, leading to pore formation contributing to release of NETs. On the other hand, when serine proteases are inhibited, NETs are formed by citrullination through the PAD4 pathway. This review puts together results from the last 31 years of research on the effects of PMA on the neutrophil and proposes new insights on their interpretation.

RNA-RNA interactions between SARS-CoV-2 and host benefit viral development and evolution during COVID-19 infection

Some studies reported that genomic RNA of SARS-CoV-2 can absorb a few host miRNAs that regulate immune-related genes and then deprive their function. In this perspective, we conjecture that the absorption of the SARS-CoV-2 genome to host miRNAs is not a coincidence, which may be an indispensable approach leading to viral survival and development in host. In our study, we collected five datasets of miRNAs that were predicted to interact with the genome of SARS-CoV-2. The targets of these miRNAs in the five groups were consistently enriched immune-related pathways and virus-infectious diseases. Interestingly, the five datasets shared no one miRNA but their targets shared 168 genes. The signaling pathway enrichment of 168 shared targets implied an unbalanced immune response that the most of interleukin signaling pathways and none of the interferon signaling pathways were significantly different. Protein-protein interaction (PPI) network using the shared targets showed that PPI pairs, including IL6-IL6R, were related to the process of SARS-CoV-2 infection and pathogenesis. In addition, we found that SARS-CoV-2 absorption to host miRNA could benefit two popular mutant strains for more infectivity and pathogenicity. Conclusively, our results suggest that genomic RNA absorption to host miRNAs may be a vital approach by which SARS-CoV-2 disturbs the host immune system and infects host cells.

Neutrophil and Eosinophil DNA Extracellular Trap Formation: Lessons From Pathogenic Fungi

Fungal infections represent a worldwide health problem. Fungal pathogens are responsible for a variety of conditions, including superficial diseases, allergic pathologies and potentially lethal invasive infections. Neutrophils and eosinophils have been implicated as effector cells in several pathologies. Neutrophils are major effector cells involved in the control of fungal infections and exhibit a plethora of antifungal mechanisms, such as phagocytosis, reactive oxygen species production, degranulation, extracellular vesicle formation, and DNA extracellular trap (ET) release. Eosinophils are polymorphonuclear cells classically implicated as effector cells in the pathogenesis of allergic diseases and helminthic infections, although their roles as immunomodulatory players in both innate and adaptive immunity are currently recognized. Eosinophils are also endowed with antifungal activities and are abundantly found in allergic conditions associated with fungal colonization and sensitization. Neutrophils and eosinophils have been demonstrated to release their nuclear and mitochondrial DNA in response to many pathogens and pro-inflammatory stimuli. ETs have been implicated in the killing and control of many pathogens, as well as in promoting inflammation and tissue damage. The formation of ETs by neutrophils and eosinophils has been described in response to pathogenic fungi. Here, we provide an overview of the mechanisms involved in the release of neutrophil and eosinophil ETs in response to fungal pathogens. General implications for understanding the formation of ETs and the roles of ETs in fungal infections are discussed.

The Msp Protein of Treponema denticola Interrupts Activity of Phosphoinositide Processing in Neutrophils

Periodontal disease is a significant health burden, causing tooth loss and poor oral and overall systemic health. Dysbiosis of the oral biofilm and a dysfunctional immune response drive chronic inflammation, causing destruction of soft tissue and alveolar bone supporting the teeth. Treponema denticola, a spirochete abundant in the plaque biofilm of patients with severe periodontal disease, perturbs neutrophil function by modulating appropriate phosphoinositide (PIP) signaling. Through a series of immunoblotting and quantitative PCR (qPCR) experiments, we show that Msp does not alter the gene transcription or protein content of key enzymes responsible for PIP3 signaling: 3' phosphatase and tensin homolog (PTEN), phosphatidylinositol 3-kinase (PI3K), or 5' Src homology 2 domain-containing inositol phosphatase 1 (SHIP1). Instead, using immunoblotting and enzyme-linked immunosorbent assays (ELISAs), we found that Msp activates PTEN through dephosphorylation specifically at the S380 site. Msp in intact organisms or outer membrane vesicles also restricts PIP signaling. SHIP1 phosphatase release was assessed using chemical inhibition and immunoprecipitation to show that Msp moderately decreases SHIP1 activity. Msp also prevents secondary activation of the PTEN/PI3K response. We speculate that this result is due to the redirection of the PIP3 substrate away from SHIP1 to PTEN. Immunofluorescence microscopy revealed a redistribution of PTEN from the cytoplasm to the plasma membrane following exposure to Msp, which may contribute to PTEN activation. Mechanisms of how T. denticola modulates and evades the host immune response are still poorly described, and here we provide further mechanistic evidence of how spirochetes modify PIP signaling to dampen neutrophil function. Understanding how oral bacteria evade the immune response to perpetuate the cycle of inflammation and infection is critical for combating periodontal disease to improve overall health outcomes.

Label-Free Proteomic Analysis Reveals Parasite-Specific Protein Alterations in Macrophages Following Leishmania amazonensis, Leishmania major, or Leishmania infantum Infection

Leishmania is an obligate intracellular parasite known to modulate the host cell to survive and proliferate. However, the complexity of host-parasite interactions remains unclear. Also, the outcome of the disease has been recognized to be species-specific and dependent on the host's immune responses. Proteomics has emerged as a powerful tool to investigate the host-pathogen interface, allowing us to deepen our knowledge about infectious diseases. Quantification of the relative amount of proteins in a sample can be achieved using label-free proteomics, and for the first time, we have used it to quantify Leishmania-specific protein alterations in macrophages. Protein extracts were obtained and digested, and peptides were identified and quantified using nano-LC coupled with tandem mass spectrometry analyses. Protein expression was validated by Western blot analysis. Integrated Proteomics Pipeline was used for peptide/protein identification and for quantification and data processing. Ingenuity Pathway Analysis was used for network analysis. In this work, we investigated how this intracellular parasite modulates protein expression on a host macrophage by comparing three different Leishmania species- L. amazonensis, one of the causative agents of cutaneous disease in the Amazon region; L. major, another causative agent of cutaneous leishmaniasis in Africa, the Middle East, China, and India; L. infantum, the causative agent of visceral leishmaniasis affecting humans and dogs in Latin America-and lipopolysaccharide stimulated macrophages as an in vitro inflammation model. Our results revealed that Leishmania infection downregulates apoptosis pathways while upregulating the activation of phagocytes/leukocytes and lipid accumulation.

Genetic alterations and expression of PTEN and its relationship with cancer stem cell markers to investigate pathogenesis and to evaluate prognosis in hepatocellular carcinoma

Aims

To investigate molecular alteration and expression of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) gene in hepatocellular carcinoma (HCC), and to evaluate the correlation between PTEN and cancer stem cell (CSC) markers and the prognostic value of these markers.

Methods

We evaluated changes of PTEN and CSC markers (CD133, epithelial cell adhesion molecule (EpCAM) and CK19) in 183 resection specimens by immunohistochemistry (IHC) and detected PTEN and phosphoinositide-3-kinase catalytic-alpha (PIK3CA) gene by fluorescence in situ hybridisation (FISH) in some specimens.

Results

PTEN and CD133, EpCAM and CK19 in 183 resection specimens were studied by IHC, and PTEN and PIK3CA genes were detected by FISH. PTEN expression was reduced in 92 HCC tissues (50.3%). There were 16 HCCs with PTEN deletion (51.6%). Comparison between PTEN IHC and FISH showed that the analysis was highly concordant (54/59, 91.5%). There were 19 HCCs with PIK3CA amplification. Deletion of PTEN was positively correlated with amplification of PIK3CA. Positive expression of CD133, EpCAM and CK19 was correlated with steatosis, moderate to poor differentiation, and so on. Reduction of PTEN expression was negatively correlated with positive expression of CD133, EpCAM and CK19. Reduced expression of PTEN (p=0.028) was an independent predictor for HCC recurrence and overall survival in HCC. PTEN−/CD133+ group had shorter OS and RFS time.

Conclusions

PTEN plays a key role in hepatocarcinogenesis and reduction of PTEN expression is related to increased expression of CD133, EpCAM and CK19, which is a useful tool to evaluate HCC prognosis and recurrence.

Tied up: Does altering phosphoinositide-mediated membrane trafficking influence neurodegenerative disease phenotypes?

Phosphoinositides are a class of membrane lipids that are found on several intracellular compartments and play diverse roles inside cells, such as vesicle formation, protein trafficking, endocytosis etc. Intracellular distribution and levels of phosphoinositides are regulated by enzymes that generate and breakdown these lipids as well as other proteins that associate with phosphoinositides. These events lead to differing levels of specific phosphoinositides on different intracellular compartments. At these intracellular locations, phosphoinositides and their associated proteins, such as Rab GTPases, dynamin and BAR domain-containing proteins, regulate a variety of membrane trafficking pathways. Neurodegenerative phenotypes in disorders such as Parkinson's disease (PD) can arise as a consequence of altered or hampered intracellular trafficking. Altered trafficking can cause proteins such as α-synuclein to aggregate intracellularly. Several trafficking pathways are regulated bymaster regulators such as LRRK2,which is known to regulate the activity of phosphoinositide effector proteins. Perturbing either the levels of phosphoinositides or their interactions with different proteins disrupts intracellular trafficking pathways, contributing to phenotypes often observed in disorders such as Alzheimer's or PDs. Thus, studying phosphoinositide regulation and its role in trafficking can give us a deeper understanding of the contribution of disrupted trafficking to neurodegenerative phenotypes.

Regulation of Hematopoietic Cell Development and Function Through Phosphoinositides

One of the most paramount receptor-induced signal transduction mechanisms in hematopoietic cells is production of the lipid second messenger phosphatidylinositol(3,4,5)trisphosphate (PIP₃) by class I phosphoinositide 3 kinases (PI3K). Defective PIP₃ signaling impairs almost every aspect of hematopoiesis, including T cell development and function. Limiting PIP₃ signaling is particularly important, because excessive PIP₃ function in lymphocytes can transform them and cause blood cancers. Here, we review the key functions of PIP₃ and related phosphoinositides in hematopoietic cells, with a special focus on those mechanisms dampening PIP₃ production, turnover, or function. Recent studies have shown that beyond “canonical” turnover by the PIP₃ phosphatases and tumor suppressors phosphatase and tensin homolog (PTEN) and SH2 domain-containing inositol-5-phosphatase-1 (SHIP-1/2), PIP₃ function in hematopoietic cells can also be dampened through antagonism with the soluble PIP₃ analogs inositol(1,3,4,5)tetrakisphosphate (IP₄) and inositol-heptakisphosphate (IP₇). Other evidence suggests that IP₄ can promote PIP₃ function in thymocytes. Moreover, IP₄ or the kinases producing it limit store-operated Ca²⁺ entry through Orai channels in B cells, T cells, and neutrophils to control cell survival and function. We discuss current models for how soluble inositol phosphates can have such diverse functions and can govern as distinct processes as hematopoietic stem cell homeostasis, neutrophil macrophage and NK cell function, and development and function of B cells and T cells. Finally, we will review the pathological consequences of dysregulated IP₄ activity in immune cells and highlight contributions of impaired inositol phosphate functions in disorders such as Kawasaki disease, common variable immunodeficiency, or blood cancer.

The inositol pyrophosphate pathway in health and diseases

Inositol pyrophosphates (IPPs) are present in organisms ranging from plants, slime moulds and fungi to mammals. Distinct classes of kinases generate different forms of energetic diphosphate-containing IPPs from inositol phosphates (IPs). Conversely, polyphosphate phosphohydrolase enzymes dephosphorylate IPPs to regenerate the respective IPs. IPPs and/or their metabolizing enzymes regulate various cell biological processes by modulating many proteins via diverse mechanisms. In the last decade, extensive research has been conducted in mammalian systems, particularly in knockout mouse models of relevant enzymes. Results obtained from these studies suggest impacts of the IPP pathway on organ development, especially of brain and testis. Conversely, deletion of specific enzymes in the pathway protects mice from various diseases such as diet-induced obesity (DIO), type-2 diabetes (T2D), fatty liver, bacterial infection, thromboembolism, cancer metastasis and aging. Furthermore, pharmacological inhibition of the same class of enzymes in mice validates the therapeutic importance of this pathway in cardio-metabolic diseases. This review critically analyses these findings and summarizes the significance of the IPP pathway in mammalian health and diseases. It also evaluates benefits and risks of targeting this pathway in disease therapies. Finally, future directions of mammalian IPP research are discussed.

Inositol in the MAnaGemENt of abdominal aortic aneurysm (IMAGEN): study protocol for a randomised controlled trial

Background

An abdominal aortic aneurysm (AAA) is a focal dilation of the abdominal aorta and is associated with a risk of fatal rupture. Experimental studies suggest that myo-inositol may exert beneficial effects on AAAs through favourable changes to biological pathways implicated in AAA pathology. The aim of the Inositol in the MAnaGemENt of abdominal aortic aneurysm (IMAGEN) trial is to assess if myo-inositol will reduce AAA growth.

Methods/design

IMAGEN is a multi-centre, prospective, parallel-group, randomised, double-blind, placebo-controlled trial. A total of 164 participants with an AAA measuring ≥ 30 mm will be randomised to either 2 g of myo-inositol or identical placebo twice daily for 12 months. The primary outcome measure will be AAA growth estimated by increase in total infrarenal aortic volume measured on computed tomographic scans. Secondary outcome measures will include AAA diameter assessed by computed tomography and ultrasound, AAA peak wall stress and peak wall rupture index, serum lipids, circulating AAA biomarkers, circulating RNAs and health-related quality of life. All analysis will be based on the intention-to-treat principle at the time of randomisation. All patients who meet the eligibility criteria, provide written informed consent and are enrolled in the study will be included in the primary analysis, regardless of adherence to dietary allocation.

Discussion

Currently, there is no known medical therapy to limit AAA progression. The IMAGEN trial will be the first randomised trial, to our knowledge, to assess the value of myo-inositol in limiting AAA growth.

Trial registration

Australian New Zealand Clinical Trials Registry, ACTRN12615001209583. Registered on 6 November 2015.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-2304-x) contains supplementary material, which is available to authorized users.

The C-terminal region of the major outer sheath protein of Treponema denticola inhibits neutrophil chemotaxis

Treponema denticola is an oral spirochete strongly associated with severe periodontal disease. A prominent virulence factor, the major outer sheath protein (Msp), disorients neutrophil chemotaxis by altering the cellular phosphoinositide balance, leading to impairment of downstream chemotactic events including actin rearrangement, Rac1 activation, and Akt activation in response to chemoattractant stimulation. The specific regions of Msp responsible for interactions with neutrophils remain unknown. In this study, we investigated the inhibitory effect of truncated Msp regions on neutrophil chemotaxis and associated signaling pathways. Murine neutrophils were treated with recombinant protein truncations followed by assessment of chemotaxis and associated signal pathway activation. Chemotaxis assays indicate sequences within the C-terminal region; particularly the first 130 amino acids, have the strongest inhibitory effect on neutrophil chemotaxis. Neutrophils incubated with the C-terminal region protein also demonstrated the greatest inhibition of Rac1 activation, increased phosphoinositide phosphatase activity, and decreased Akt activation; orchestrating impairment of chemotaxis. Furthermore, incubation with antibodies specific to only the C-terminal region blocked the Msp-induced inhibition of chemotaxis and denaturing the protein restored Rac1 activation. Msp from the strain OTK, with numerous amino acid substitutions throughout the polypeptide, including the C-terminal region compared with strain 35405, showed increased ability to impair neutrophil chemotaxis. Collectively, these results indicate that the C-terminal region of Msp is the most potent region to modulate neutrophil chemotactic signaling and that specific sequences and structures are likely to be required. Knowledge of how spirochetes dampen the neutrophil response is limited and Msp may represent a novel therapeutic target for periodontal disease.

Metagenomic Shotgun Sequencing and Unbiased Metabolomic Profiling Identify Specific Human Gut Microbiota and Metabolites Associated with Immune Checkpoint Therapy Efficacy in Melanoma Patients

This is the first prospective study of the effects of human gut microbiota and metabolites on immune checkpoint inhibitor (ICT) response in metastatic melanoma patients. Whereas many melanoma patients exhibit profound response to ICT, there are fewer options for patients failing ICT-particularly with BRAF-wild-type disease. In preclinical studies, specific gut microbiota promotes regression of melanoma in mice. We therefore conducted a study of the effects of pretreatment gut microbiota and metabolites on ICT Response Evaluation Criteria in Solid Tumors response in 39 metastatic melanoma patients treated with ipilimumab, nivolumab, ipilimumab plus nivolumab (IN), or pembrolizumab (P). IN yielded 67% responses and 8% stable disease; P achieved 23% responses and 23% stable disease. ICT responders for all types of therapies were enriched for Bacteroides caccae. Among IN responders, the gut microbiome was enriched for Faecalibacterium prausnitzii, Bacteroides thetaiotamicron, and Holdemania filiformis. Among P responders, the microbiome was enriched for Dorea formicogenerans. Unbiased shotgun metabolomics revealed high levels of anacardic acid in ICT responders. Based on these pilot studies, both additional confirmatory clinical studies and preclinical testing of these bacterial species and metabolites are warranted to confirm their ICT enhancing activity.

Oxidative stress induced by Se-deficient high-energy diet implicates neutrophil dysfunction via Nrf2 pathway suppression in swine

The mechanism of the interaction between Se deficiency and high energy remains limited. The aim of the current study was to identify whether Se-deficient, high-energy diet can induce oxidative stress, and downregulate the Nrf2 pathway and phagocytic dysfunction of neutrophils. We detected the phagocytic activity, ROS production, protein levels of Nrf2 and Nrf2 downstream target genes, and the mRNA levels of 25 selenoproteins, heat shock proteins, and cytokines in neutrophils. Cytokine ELISA kits were used to measure the serum cytokines. The concentration of ROS was elevated (P < 0.05) in obese swine fed on a low Se diet (less than 0.03 mg/kg Se) compared to control swine. The protein levels of Nrf2 and its downstream target genes were depressed during Se deficiency and high-energy intake. The mRNA levels of 16 selenoproteins were significantly decreased (P < 0.05) in the Se-deficient group and Se-deficient, high-energy group compared to the control group. However, the mRNA levels of 13 selenoproteins in peripheral blood neutrophils were upregulated in high energy group, except TrxR1, SelI and SepW. In summary, these data indicated that a Se-deficient, high-energy diet inhibits the Nrf2 pathway and its regulation of oxidative stress, and prompted a pleiotropic mechanism that suppresses phagocytosis.

High performance mass spectrometry based proteomics reveals enzyme and signaling pathway regulation in neutrophils during the early stage of surgical trauma

PURPOSE

In clinical conditions trauma is associated with high mortality and morbidity. Neutrophils play a key role in the development of multiple organ failure after trauma EXPERIMENTAL DESIGN: To have a detailed understanding of the neutrophil activation at primary stages after trauma, neutrophils are isolated from control and surgical trauma rats in this study. Extracted proteins are analyzed using nano liquid chromatography coupled with tandem mass spectrometry.

RESULTS

A total of 2924 rat neutrophil proteins are identified in our analysis, of which 393 are found differentially regulated between control and trauma groups. By using functional pathways analysis of the 190 proteins up-regulated in surgical trauma, we found proteins related to transcription initiation and protein biosynthesis. On the other hand, among the 203 proteins down-regulated in surgical trauma we found enrichment for proteins of the immune response, proteasome degradation and actin cytoskeleton. Overall, enzyme prediction analysis revealed that regulated enzymes are directly involved in neutrophil apoptosis, directional migration and chemotaxis. Our observations are then confirmed by in silico protein-protein interaction analysis.

CONCLUSIONS AND CLINICAL RELEVANCE

Collectively, our results reveal that neutrophils drastically regulate their biochemical pathways after the early stages of surgical trauma, showing lower activity. This implies higher susceptibility of the trauma patients to infection and bystander tissues damage.

Immunoreceptors on neutrophils

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Neutrophil activities must be tightly controlled to maintain immune homeostasis.

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Activating and inhibitory receptors balance the outcome of immune cell activation.

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Immunoreceptors contain Ig-like extracellular domains and signal via ITAMs or ITIMs.

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Syk or SHP/SHIP mediate downstream signaling after immunoreceptor activation.

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Targeting immunoreceptors provides opportunities for therapeutic interventions.

Neutrophils play a critical role in the host defense against infection, and they are able to perform a variety of effector mechanisms for this purpose. However, there are also a number of pathological conditions, including autoimmunity and cancer, in which the activities of neutrophils can be harmful to the host. Thus the activities of neutrophils need to be tightly controlled. As in the case of other immune cells, many of the neutrophil effector functions are regulated by a series of immunoreceptors on the plasma membrane. Here, we review what is currently known about the functions of the various individual immunoreceptors and their signaling in neutrophils. While these immunoreceptors allow for the recognition of a diverse range of extracellular ligands, such as cell surface structures (like proteins, glycans and lipids) and extracellular matrix components, they commonly signal via conserved ITAM or ITIM motifs and their associated downstream pathways that depend on the phosphorylation of tyrosine residues in proteins and/or inositol lipids. This allows for a balanced homeostatic regulation of neutrophil effector functions. Given the number of available immunoreceptors and their fundamental importance for neutrophil behavior, it is perhaps not surprising that pathogens have evolved means to evade immune responses through some of these pathways. Inversely, some of these receptors evolved to specifically recognize these pathogens. Finally, some interactions mediated by immunoreceptors in neutrophils have been identified as promising targets for therapeutic intervention.

Inositol(1,4,5)P3 3-kinase isoenzymes: Catalytic properties and importance of targeting to F-actin to understand function

Inositol(1,4,5)trisphosphate (Ins(1,4,5)P3) 3-kinases (Itpks) catalyze the phosphorylation of inositol(1,4,5)trisphosphate into inositol(1,3,4,5)tetrakisphosphate (Ins(1,3,4,5)P4). Three isoenzymes Itpka/b and c have been identified in human, rat and mouse. They share a catalytic domain relatively well conserved at the C-terminal end and a quite isoenzyme specific regulatory domain at the N-terminal end of the protein. Activity determined in cell homogenates with Ins(1,4,5)P3 and ATP as substrate is generally very low compared to Ins(1,4,5)P3 5-phosphatase, except in a few tissues such as brain, testis, thymus or intestine. Activity is very much Ca(2+) sensitive and increased in the presence of Ca(2+)/calmodulin (CaM) as compared to EGTA alone. When challenged after receptor activation, activity could be further activated several fold, e.g. in rat brain cortical slices stimulated by carbachol or in human astrocytoma cells stimulated by purinergic agonists. Two of the three isoenzymes show an unexpected cytoskeletal localization for Itpka/b or at the leading edge for Itpkb. This is explained by the presence of an F-actin binding site at the N-terminal part of the two isoenzymes. This interaction confers to Itpka the properties of an F-actin bundling protein with two major consequences: i) it can reorganize the cytoskeletal network, particularly in dendritic spines, and ii) can provide an opportunity for Ins(1,3,4,5)P4 to act very locally as second messenger.